Technical Field
The present invention relates to an apparatus and method for attaching a vacuum pump to a lens barrel portion of an electron beam application apparatus such as an electron beam inspection apparatus or an electron beam lithography system which uses an electron beam.
Background Art
In an electron beam application apparatus such as an electron beam inspection apparatus or an electron beam lithography system which uses an electron beam, a main chamber incorporates a stage that holds and moves a sample such as a wafer or a mask with respect to the electron beam, and the chamber is kept in vacuum in order to ensure stability and linear stability of the electron beam. In addition, the adverse effect of magnetism needs to be minimized, and thus, a magnetic material or the like is utilized to shield (seal) the magnetism outside the main chamber from affecting the inside of the main chamber.
For a lens barrel portion installed on top of the main chamber, the cylinder itself of the lens barrel portion is also formed of a magnetic material. In addition, the lens barrel portion connects to a vacuum pump such as a turbomolecular pump which can evacuate and place the lens barrel portion in a high vacuum.
When the lens barrel portion is evacuated and placed in a high vacuum using the vacuum pump, the following conditions need to be met.
(1) For the evacuation, with evacuation resistance between an evacuation target area (the inside of the lens barrel portion) and a vacuum pump intake port taken into account, the original evacuation performance of the pump needs to be fully delivered by maximizing a conductance corresponding to the inverse of the evacuation resistance.
(2) For the turbomolecular pump, a magnetic bearing utilizing an electromagnet is often adopted which supports rotation of a rotor without creating friction and which is suitable for high speed rotations. Furthermore, the turbomolecular pump includes a motor to rotationally drive the rotor. Thus, during operation of the pump, a magnetic field is generated by the magnetic bearing and the motor. Full consideration is needed for a configuration in which the pump is installed with respect to the lens barrel portion that is particularly desirably prevented from being affected by magnetism.
(3) In order to be prevented from being affected by vibration, which may affect performance and functions, the lens barrel portion is placed on a vibration damping apparatus (vibration damping base) along with the main chamber to reduce vibration transmitted from a floor on which the lens barrel portion is installed. The vertical and horizontal positions of the vibration damping apparatus during operation (while the electron beam application apparatus is rising) differ slightly from the vertical and horizontal positions of the vibration damping apparatus during non-operation (while the electron beam application apparatus is seated). Furthermore, the rotor of the turbomolecular pump rotates at high speed, and thus, the adverse effect, on the lens barrel portion, of vibration generated by the turbomolecular pump can desirably be maximally eliminated. Therefore, the lens barrel portion needs to be elastically connected to the vacuum pump such as the turbomolecular pump.
On the other hand, the turbomolecular pump is a high-speed rotating machine, and thus, if abnormality such as rotor lock or rotor destruction occurs during operation, an excessive force acts not only on the pump itself but also on, for example, an attached portion of the pump. Then, if, for example, a fixed portion of the pump has an insufficient strength, the pump may slip off. This may damage surrounding apparatuses. Moreover, a magnetic-bearing turbomolecular pump is characterized by being susceptible to external vibration with a low frequency. Thus, the turbomolecular pump needs to be mounted on a structure with a sufficient rigidity so as to maintain a sufficient strength.
Therefore, the lens barrel portion and the intake port of the vacuum pump need to be elastically connected together, and the fixed portion of the vacuum pump needs to be mounted on a fixation side such as the floor so as to ensure sufficient rigidity.
When an upper area of the lens barrel portion is to be evacuated, a related technique uses a configuration (hereinafter referred to as a “configuration A”) in which the lens barrel portion is connected to the intake port via a bellows to insulate vibration and in which the vacuum pump is suspended by the bellows. For example, both Japanese Patent Laid-Open No. 2012-112255 and Japanese Patent Laid-Open No. 2008-232029 disclose the configuration A in which the turbomolecular pump is suspended from an electron beam application apparatus via the bellows.
The configuration A will be described below with reference to FIG. 6. In an electron beam application apparatus 10, an electron beam is constricted inside a lens barrel portion 12. The constricted electron beam is delivered to a sample disposed in a main chamber 14. The lens barrel portion 12 is kept in a high vacuum by a vacuum pump 16. Furthermore, the main chamber 14 is also kept in a high vacuum by another vacuum pump (not shown in the drawings). A sample stage that moves the sample is mounted in the main chamber 14. The main chamber 14 is mounted on a vibration damping base 18 that is disposed on a floor 20 serving as a base. Thus, the vibration damping base 18 dampens floor vibration or air vibration transmitted to the main chamber 14.
When the vacuum pump 16 is operated during operation of the electron beam application apparatus 10, vibration may occur, which may reduce the accuracy of inspection, lithography, or the like which is performed by the electron beam application apparatus 10. Thus, an evacuation connection portion 22 and a vibration absorbing portion 24 connected to the evacuation connection portion 22 are provided between the lens barrel portion 12 and the vacuum pump 16. The vibration absorbing portion 24 is a bellows or the like which is a coupling member with a low rigidity (elasticity). Vibration is isolated via the vibration absorbing portion 24. The vibration absorbing portion 24 is connected to the evacuation connection portion 22 and the vacuum pump 16 by flanges 26 provided at the respective opposite ends of the vibration absorbing portion 24. The vacuum pump 16 is connected to the vibration absorbing portion 24 by an intake port 28 of the vacuum pump 16.
Japanese Patent Laid-Open No. 2002-303294 discloses, in FIG. 2 thereof, the configuration A in which the turbomolecular pump is suspended from the electron beam application apparatus via the bellows. The turbomolecular pump is fixed to the floor via a spring hanging downward from a bottom portion of the pump. That is, the top and bottom of the vacuum pump are elastically fixed.
On the other hand, when a lower area of the lens barrel portion is to be evacuated, a configuration (hereinafter referred to as a “configuration B”) is used in which the bellows and the pump are held in a horizontal direction, with the bellows connected to the electron beam application apparatus.
The configuration B will be described below with reference to FIG. 7. The same components are hereinafter denoted by the same reference numerals. In an electron beam application apparatus 29, an electron beam is constricted inside a lens barrel portion 12A. The constricted electron beam is then delivered to a sample disposed in the main chamber 14. The lens barrel portion 12 is kept in a high vacuum by a vacuum pump 16A.
When the vacuum pump 16A is operated during operation of the electron beam application apparatus 29, vibration may occur, which may reduce the accuracy of inspection performed by the electron beam application apparatus 29. Thus, the vibration absorbing portion 24 is provided between the lens barrel portion 12A and the vacuum pump 16A. The vibration absorbing portion 24 is connected to the lens barrel portion 12A and the vacuum pump 16A by the flanges 26 provided at the respective opposite ends of the vibration absorbing portion 24. The vacuum pump 16A is connected to the vibration absorbing portion 24 by the intake port 28 and fixed to a vacuum pump fixing structure 30. The vacuum pump fixing structure 30 is fixed to the floor 20.
For example, Japanese Patent Laid-Open No. 2003-282423 is an example in which the main chamber located below the lens barrel portion is evacuated. Japanese Patent Laid-Open No. 2003-282423 discloses, in FIG. 8 thereof, an example in which the vacuum pump is connected to the electron beam application apparatus via a bellows 40A.
Japanese Patent Laid-Open No. HEI 08-329874 discloses that the vacuum pump is fixed to a lower surface of the electron beam application apparatus. However, Japanese Patent Laid-Open No. HEI 08-329874 fails to disclose where the bellows is disposed.
In the configuration A according to the related technique, the fixing strength of the pump is disadvantageously insufficient during rotor lock and the like. Moreover, disadvantageously, the magnetic-bearing turbomolecular pump is susceptible to external vibration with a low frequency, and the configuration A in which the magnetic-bearing turbomolecular pump is less rigidly suspended offers low resistance to external vibration. In the configuration B according to the related technique, the bellows extends and contracts between a state in which the bellows is internally in vacuum and a state in which the bellows is internally at the atmospheric pressure. Thus, disadvantageously, an external force is applied to the lens barrel portion placed on the vibration damping apparatus.